This invention relates to a method for chemically treating karaya gum. More particularly this invention relates to a method of treating karaya gum to improve its properties so that when used as a constituent of a plastic priming mixture, it will improve the extrudable character and rheological stability of such mixtures to enable their use in the mechanical charging of primers.
The use of karaya gum as an adhesive or binder in priming compositions is disclosed in U.S. Pat. No. 3,423,259. That patent also discloses that besides the adhesive or binder action, karaya gum provides a means of controlling the fluidity of wet priming compositions and a means of retaining water in the mixture so that separation of water from the crystalline and granular solids of the priming composition in the mixture does not occur.
U.S. Pat. No. 3,423,259 also mentions that priming mixtures prepared with karaya gum can be wetted sufficiently without encountering separation of the solid and liquid phases to provide the fluidity required for the extrusion of the bulk material. The patent further states that such mixtures are sufficiently plastic and will flow readily enough to permit feeding of the bulk material into a pellet forming mechanism capable of charging primers mechanically. A method and mechanism for mechanically charging primers by an extrusion process is more fully set forth in copending application, Ser. No. 253,481, filed May 15, 1972, now U.S. Pat. No. 3,820,578.
In the subsequent development of the mechanical charging process it became evident that with some types of priming compositions, particularly with respect to center fire priming compositions, a properly extrudable composition having sufficiently long pot life cannot be obtained by simply including karaya gum in the formulation. The difficulty appeared to be the result of the incompatability of the karaya gum with one or more of the materials in the primer formulation. Such incompatability was manifested by a decrease of viscosity and/or lubricity of the gum dispersion on exposure to the compounds present in these priming compositions. Viscosity of the gum dispersion is essential for retention of water in the mixture to prevent the settling of solids and the separation of water. Lubricity permits the granular and crystalline particles of priming composition to slide by each other readily avoiding the occurrence of a tendency for packing or "bridging." Both of these factors are important in imparting extrudable character to the priming mixtures. Ideally, an extrudable priming mixture should contain karaya gum in the amount of 1-2% of the total solids by weight and about 16-17% water. However, with certain priming compositions, the presence of certain ingredients caused a significant lowering of the viscosity of the mixture rendering it unsuitable for extruding.
If additional karaya gum is added to compensate for the loss of viscosity and added karaya gum would have a deleterious effect upon the dried priming composition resulting in a significant loss in the sensitivity. With the present invention, the karaya gum is treated to improve its compatability with various compounds of primer compositions so that substantially less than 3% of karaya gum can be used to avoid this deleterious effect.